Atherosclerosis is a risk factor frequently associated with thrombosis. In laboratory studies, certain oral streptococci induce aggregation of human platelet rich plasma into in vitro thrombi. Since these microbes probably contribute to recurrent, otherwise asymptomatic, bacteremias through life, the hypothesis that Streptococcus sanguis may be a thrombogenic trigger in atherosclerotic vascular diseases will be tested in mammals. Specifically, in this pilot project, techniques will be learned to: 1. induce atherosclerosis by established protocols in rabbits and dogs; 2. inject platelet-interactive S. sanguis intravenously; and 3. follow the development and consequences of thrombosis. Development of atherosclerosis will be followed by monitoring blood cholesterol and, later, postmortem verification. Bacteremias, both background and experimental, will be verified by blood cultures. Thrombosis will be identified by following the fate of IIIIn-labeled platelets with external scans and confirmed by postmortem examination. Altered hemodynamics of organs with lesions will be studied by a microsphere distribution method and electrocardiography.